Take care though, because a lot of security hole exists if you dont setup things right, as this is a powerful tool and "with great power comes great responsibility" ;)
Note that this tutorial is for traditional systems, if you have ACL (Access Control Lists), you need to give the respective to suid permission.

Solution 1:
Security-wise the better one: If you want to su to one or two particular user(s),
have one or two files that suid to those users.
If you have more users, depending on what you are doing, create a user group, and use the group.

Solution 2:
The simplest one sometimes: have the file suid to root. THIS IS ESPECIALLY DANGEROUS,
avoid it.